1. Field of the Invention
The present invention relates to a power ultrasonic transducer, and more particularly, to a power ultrasonic transducer which is used for the execution of ultrasonic cleaning, the promotion of chemical reaction and the like.
2. Discussion of Related Art
Generally, a conventional Langevin type transducer, which is configured to insert a piezoelectric element between two metals and to be secured by a bolt, has been widely used in this field. However, since this type of transducer can not be directly used in the water, it should be used only in case of being attached on a wall surface of a cleaning vessel. In addition, since the Langevin type transducer generates an ultrasonic wave by utilizing a longitudinal vibration, this results in the limitation of ultrasonic power generated from the transducer.
In the Langevin type transducer, hence, there occurs a disadvantage in that transducer array should be used so as to produce a high power. In this case, if these transducers are not synchronized with each other during operating period, the life of the adjacent transducers influenced by the distortion force generated from the vibration of any specific transducer can be shortened.
On the other hand, another research is executed by U.S. Pat. No. 4,537,511 (in 1985) which improves the above problems suffered from the conventional Langevin type transducer. This is an improved transducer which can produce a high power and is directly used in the water. In this effort, the transducer includes an ultrasonic generator which has a longitudinal vibration mode by using a piezoelectric element and a hollow type rod which has a length of integer(n) times of half wavelength(lambda/2) and is coupled to the end of one side of the ultrasonic generator, to thereby radiate the ultrasonic wave in a radial direction.
However, the transducer according to the U.S. Pat. No. 4,537,511 can produce a higher power, when compared with the conventional Langevin type transducer, but since the other end of the hollow type rod as a free end is exposed into a medium, an undesired ultrasonic wave in a longitudinal direction is radiated, which of course results in the loss of energy.
To solve this problem, another research is executed by U.S. Pat. No. 5,200,666 (in 1993) and European Pat. No. EP 455837 (in 1991), wherein a piezo type ultrasonic generator is attached on the both end sides of a hollow type rod, respectively, to thereby generate an higher ultrasonic power in a radial direction. Here, the hollow type rod has a length of integer(n) times of half wavelength(lambda/2), in the same manner as the above.
In this case, if the characteristics such as the resonant frequencies and impedances of the two end-sided ultrasonic generators are not accurately consistent with each other, there exists a difference in phases and amplitudes of the longitudinal vibration generated from each of the two ultrasonic generators, so the efficiency of the transducer is inevitably reduced. Meanwhile, upon manufacturing of the transducer, it is very difficult to make two ultrasonic generators have equal characteristics.
On the other hand, FIG. 3 is a perspective view of a prior art transducer introduced by Uchino, which has a quite different structure and application from the conventional transducers as mentioned above. The disc-shaped transducer which is reported by Uchino in IEEE Vol. 44, No. 3,1997, pp. 597-605, 1997, is results in the increment of displacement thereof. In this effort, the shape of body (brass endcap) is newly designed, thus to allow the transducer to increase the ultrasonic power.
However, the transducer by Uchino takes a disc type having a diameter of about 10 mm and is used for a small actuator. Further, since the transducer includes the ultrasonic generator which is comprised only of a piezoceramic having about 1 mm in thickness and about 10 mm in diameter and utilizes a radial mode of the piezoceramic, it is apparent that it is difficult to manufacture the piezoceramic of the same thickness having about 50 mm or more in diameter. This results in a fundamental limitation in the increment of ultrasonic power from the transducer.